Effects of Dietary Menhaden Oil, Soy and a Cyclooxygenase Inhibitor on Human Breast Cancer Cell Growth and Metastasis in Nude Mice

The purpose of Study 1 was to examine the effect of dietary soy on the progression of MDA-MB-435 human breast cancer cell solid tumours in nude mice. When toasted soy chips were fed at levels of 5%, 10% or 20% (wt/wt) in a high fat, linoleic acid-rich diet for 12 weeks, there was a trend for larger mammary fat pad tumours to occur with increasing soy intake. However, compared with the controls the severity of macroscopic lung metastasis was reduced significantly in the groups fed 10% and 20% soy. Study 2 compared the effects of diets containing 23% corn oil (CO), 18% menhaden oil (M)) + 5% CO, 18% MO + 5% CO + 10% soy chips and MO or soy-supplemented diets + indomethacin treatment in the same animal model. Feeding the 18% MO diet without soy or indomethacin reduced primary tumour growth; statistically significant effects were not observed in any of the other groups. All three of the groups with MO supplementation showed a reduction in the occurrence and severity of macroscopic lung metastases, together with the expected decreases in tumour prostaglandin E levels. These effects were most pronounced when MO was combined with indomethacin treatment. When indomethacin was given with dietary soy, the previously reported suppressive effect of the cyclooxygenase inhibitor on MDA-MB-435 cell tumour progression was lost, despite reductions in tumour prostaglandin E concentrations.

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"there was a trend for larger tumours with increasing soy intake"

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